The present invention relates to the field of inscribing indicia on a surface of gemstones, and more particularly to a system employing a Q-switched pulse laser for forming markings on a portion of a gemstone.
A known system, as described in U.S. Pat. No. 4,392,476, incorporated herein by reference, for inscribing diamonds includes a Nd:YAG (1.06 xcexcm, frequency doubled) Q-switched laser which marks diamonds by graphitizing the surface at a laser focal point. The beam position is computer controlled to create overlapping treated regions. The accuracy of known embodiments of this system are limited by vibration and laser steering system accuracy.
U.S. Pat. No. 4,467,172, incorporated herein by reference, describes a laser beam diamond inscribing system, which provides a Q-switched flashlamp pumped YAG laser (1.06 xcexcm, frequency doubled) with the diamond mounted on a computer-controlled positioning table for inscribing alphanumeric characters. See also, U.S. Pat. Nos. 2,351,932, 3,407,364, 3,527,198, 3,622,739, 3,775,586 and 4,048,515, and foreign patents JP 00-48,489 and JP 00-77,989
U.S. Pat. Nos. 5,410,125 and 5,149,938 describe systems which produce a gemstone marking by employing an excimer laser (193 nm) with a masked marking image. Thus, repositioning to form complete characters or graphics is unnecessary. The diamond selectively absorbs the excimer laser radiation and undergoes a partial allotropic transformation without losing its diamond crystal lattice configuration. See also, U.S. Pat. Nos. 3,527,198 and 4,401,876. U.S. Pat. No. 5,410,125 is a continuation-in-part of Ser. No. 595,861, issued as U.S. Pat. No. 5,149,938.
Gemstone News, Nov. 2, 1995, xe2x80x9cSerial Numbers are Laser Inscribedxe2x80x9d, and Jeweler""s Keystone-Circular, June 1996, pp. 76 relate to gemstones inscribed with serial numbers or markings.
U.S. Pat. No. 3,537,198 relates to a method of working diamonds using laser energy. U.S. Pat. No. 5,190,024, relates to a diamond sawing process. A laser can be used both to mark and saw the diamond in one operation. See also, U.S. Pat. Nos. 671,830, 671,831, 694,215, 732,118, 732,119, 3,527,198 and 4,392,476, as well as Foreign Reference GB 122,470.
U.S. Pat. No. 4,401,876 relates to a system for kerfing a gemstone such as a diamond, employing a high energy, high pulse rate, low order mode, laser beam. See also, U.S. Pat. Nos. 3,440,388, 3,527,198 and 3,700,850, as well as foreign references BE 877,326, DE 130,138, DE 133,023, GB 1,057,127, GB 1,059,249, GB 1,094,367, GB 1,254,120, GB 1,265,241, GB 1,292,981, GB 1,324,903, GB 1,326,775, GB 1,377,131, GB 1,405,487, GB 1,446,806, GB 2,052,369, Laser Institute of America, xe2x80x9cGuide for Material Processing by Lasersxe2x80x9d 1978; xe2x80x9cIndustrial Diamond Reviewxe2x80x9d, March 1980, pp. 90 and 91; xe2x80x9cLaser Application Notesxe2x80x9d, 1(1) (February 1979); xe2x80x9cNew Hyperyagxe2x80x9d, on Model DLPY 4-System 2000 Yag Laser; and xe2x80x9cDiamondsxe2x80x9d: N.A.G. Press LTD, Chapter Eleven, pp. 235-242.
U.S. Pat. No. 4,799,786, incorporated herein by reference, relates to a method of diamond identification in which a sample to be identified is placed in a beam of monochromatic laser radiation of pre-determined wavelength. The scattered Raman radiation emitted from the sample is passed through a filter adapted to pass only scattered Raman radiation of frequency characteristic of a diamond. The filtered radiation is then detected by the human eye or a photocell device. See also, U.S. Pat. Nos. 4,397,556 and 4,693,377, and foreign patent GB 2,140,555, Melles Griot, Optics Guide 3, 1985, pp, 1, 333, 350, 351; and Solin et al., Physical Review B, 1(4):1687-1698 (Feb. 15, 1970).
U.S. Pat. No. 4,875,771, incorporated herein by reference, relates to a method for assessing diamond quality, by assessing diamonds with a laser Raman spectrometer. The system is initially calibrated by use of diamonds with known quality characteristics, the characteristics having been assessed, for example, by a conventional subjective procedure. Diamonds of unknown quality characteristics are then placed in the spectrometer and irradiated with laser radiation. The intensity of the scattered Raman signal from the diamond is monitored for one or more orientations of the diamond, the resultant signal being a characteristic of the diamond and believed to indicate a quality level of the diamond. See also, U.S. Pat. Nos. 3,414,354, 3,989,379, 4,259,011, 4,394,580, 4,397,556 and 4,620,284, and foreign patents FR 643,142, FR 2,496,888, JP 01-58,544, GB 1,384,813, GB 1,416,568, GB 2,010,474, GB 0,041,348 and GB 2,140,555, S. A. Solin and K. A. Ramdas, Raman Spectrum of Diamond, Physical Review vol. 1(4), pp. 1687-1698.
The aforementioned documents detail components, methods and systems which may be applied in the construction and operation of the present invention.
The present invention provides a system having a pulse laser, such as a Q-switched laser diode excited Nd:YLF laser, which produces a series of ablated or graphitized spots on the surface of a workpiece, such as a diamond gemstone. The workpiece is mounted on a translatable stage, for focusing and positioning of the beam.
The translatable stage is controlled by a computer to produce a complex marking pattern. This computer may also be used for process control and imaging, as well as other functions.
The process according to the present invention typically achieves a positioning accuracy of about xc2x11 micron. The laser and translatable mounting stage are compact and are preferably rigidly mounted on a common platform, allowing sufficient common mode vibration immunity so that only standard vibration damping need be employed rather than extraordinary damping. Therefore, simple and small passive vibration isolation mounts for the platform or chassis are employed, rather than requiring active vibration suppression systems as in known systems.
Optical feedback of the process is possible through one or more video cameras, e.g., 2 CCD imagers provided at right angles, which are provided with a field of view including the focal point of the laser. The correct positioning of the gemstone may thus be assured by correct alignment of the imagers on the workpiece. One imager is directed at the work surface along the axis of the laser, and has a focal plane including the focal point of the laser. Optical feedback through the imagers may also be used to monitor the progress of the marking process, and therefore may be used to adjust workpiece positioning as well as inscription speed, number, intensity and/or rate of pulses at a given location, as well as to verify progress of the marking process. One imager is directed to view a top portion of the workpiece, e.g., directed perpendicular to the table surface of a diamond, allowing identification of a girdle profile, while the second imager is directed to view a side portion of the workpiece, e.g., a profile, and also providing a direct view of the girdle of a gemstone. Thus, the second imager may be used to view the marking process in real time.
The optical feedback system also allows the operator to design an inscription, locate the inscription on the workpiece, verify the marking process and archive or store an image of the workpiece and formed markings.
The markings themselves may have an invariant inscription, a fully automated inscription, e.g., a serial number, a semiautomated inscription, e.g., having a fixed and variable portion, or a fully custom inscription, including graphics.
According to one embodiment, an inscription for a gemstone is defined in relation to a bar code which accompanies the packaging for the gemstone or a preprinted sheet. A bar code reader is provided for the operator to input the bar codes into a computer, without having to retype the data and with lower risk of error. Thus, an inscription may include a fixed portion, e.g., a logo or trademark, a semivariable portion, e.g., a gem rating or grading, and a hypervariable portion, e.g., a serial number. In this case, for example, a logo or trademark is preprogrammed, and inscribed on every workpiece in a series. The gem rating or grading can be scanned as a bar code, printed on a sheet associated with that gemstone, such as a receipt or label. The serial number may be automatically determined, and for example, printed on a receipt or label, and employed as a unique identifier to be applied to the stone. The inscribed characters need not be limited to alphanumeric symbols, and in fact may be fonts in any language, line-drawing characters, custom characters or pictorial representations.
The workpiece may be associated with data, stored in a medium physically associated with the workpiece or in a remote medium accessible through use of an identification of the workpiece. For example, the associated memory is a nonvolatile memory, such as a battery-backed random access memory, an electrically erasable read only memory, a ferroelectric memory, or other storage media such as magnetic stripes, rotating magnetic media, optical memories, and printed matter.
A vanity inscription may be provided on the workpiece as a custom or semicustom inscription, which may be provided as computer test, graphics or a computer-scanned image. The marking system may be employed to mark portions of a gemstone other than the girdle, for example the table. Therefore, in the case of such vanity inscriptions, the intent may be to provide a visible inscription, to enhance the sentimental value of the workpiece, rather than to provide an unobtrusive microscopic identification or authentication marking.
In many instances, it is desired that each inscribed workpiece be separately identifiable. This may be by way of a unique marking on the stone or a unique combination of marking and easily identified characteristics of the workpiece, such as weight, shape, type, etc. In one embodiment, the markings themselves form a code, such as an alphanumeric or bar code, which may be electronically or automatically read or ascertained from an examination of the workpiece.
An image of the marked workpiece may be formed or printed on a certificate which accompanies the workpiece, allowing verification that the workpiece corresponds to the certificate by studying the image in comparison with the actual workpiece. The image advantageously includes all or a portion of the marking, as well as identifiable features of the workpiece, such as landmarks, edges, facets, etc. Thus, the image may be used as a xe2x80x9cfingerprintxe2x80x9d identification of the workpiece. The image on the certificate may be formed photographically or electronically. Thus, the image as stored need not be formed through the CCD images or the marking system, and may be produced as a separate step.
Advantageously, an image of a completed marking or a bitmap of an inscription program is stored in a database, and therefore is available for comparison and later authentication of a workpiece, and to prevent inadvertent or undesired duplicate markings. The storage may be electronic or photographic, and thus the database may reside on magnetic or magnetooptical media, microfilm, paper or film, holographic crystals, magnetic or optical tape, or other known media.
In accordance with one aspect of the invention, a duplicate-prevention function is provided integral to the marking device which may not be overridden by a user, e.g., to prevent inadvertent or intentional misuse of the system. In this case, the laser system may include a lockout circuit which prevents activation of the laser control and positioning systems under unauthorized circumstances. Such a lockout may be provided in the power supply or other critical subsystem of the device.
Based on the use of the marking system, a report may be generated by the computer/controller. Because the inscription is a raster ablated image, such report may advantageously include either the programmed inscription as a graphic printout or an image received from the optical feedback imaging system, e.g., the video camera. As stated above, the report may also include or be associated with a certificate of authenticity, e.g., including a facsimile of the workpiece image including the marking. A known image authentication scheme is disclosed in U.S. Pat. No. 5,499,294, incorporated herein by reference.
The entire workpiece is generally mounted on a translatable stage, allowing precise positioning. Thus, for compact designs, the holder may accommodate workpieces of less than about 30 mm in a largest dimension, although the stage is capable of accurate positioning over a larger distance. The stage is generally translatable along three axes, X, Y, and Z in a Cartesian coordinate system, but may also include other axes, e.g., rotational axes. For example, a brilliant cut diamond is radially symmetric. Therefore, where an inscription or marking is desired around the diamond girdle, the diamond may be held in focus by adjusting a Z axial displacement and an inscription defined by translation along the X and Y axes during laser pulsing. Alternately, the diamond may be initially positioned appropriately along the X, Y and Z axes, and rotated about an axis and translated sequentially along a Y axis to define the inscription. In this case, the Z axis and possibly X axis may also be used to retain focus condition. Where X, Y and Z axes are employed for automated control, a manual rotational control is preferably provided with detents at regular intervals.
The positioning system, for moving the workpiece in relation to the laser focal point may also include or be formed from beam steering systems, such as mirrors, electrooptical elements, spatial light modulators, such as the Texas Instruments Digital Mirror Device (xe2x80x9cDMDxe2x80x9d, also known as Digital Light Processor, xe2x80x9cDLPxe2x80x9d), holographic or diffractive elements, or other optical systems. However, a translatable stage is a preferred means for directing the focused laser energy onto a desired portion of the workpiece.
The workpiece generally sits in a holder which detachably mounts to the translatable stage. Thus, a workpiece may be suitably mounted in a holder outside the apparatus while another workpiece is being inscribed. These holders may also increase the versatility of the device by providing adaptation to workpieces or various sizes and shapes. For example, round, oval, heart, marquis and other cut diamonds may each be provided with separately optimized holders; further, diamonds of various size ranges may be accommodated by differing holders, as necessary.
According to another embodiment, a mounted workpiece, e.g., a diamond in a setting, may be inscribed on portions which are not obscured. For example, in a pronged setting, a portion of the girdle may be exposed, and thus may be available for marking. In this case, a multi-articulated holder or set of holders may be provided to properly position the workpiece within the inscribing chamber of the device. Holders may be provided to accommodate mounted gems in rings, earrings, pendants, and possibly bracelets, brooches, and other common forms.
The computerized control system provides a user interface making the various functionality accessible to users, and may further limit use and operation to safe and/or desired activities. Therefore, the computerized control system may be programmed to limit activities which would damage the workpiece, circumvent security or authentication procedures, or otherwise be undesired. The computerized control system may therefore require user authentication, employ video pattern recognition of the workpiece, especially markings on the workpiece, and control operation of the laser system to avoid damage to the system components or the particular workpiece. The system may also acquire an image, fingerprint, retinal image or other secure identification of the operator.
The system may also include a diamond or gemstone analysis system for describing the quality and/or characteristics of the workpiece. This analysis may be employed by the system in order to optimize the marking process, generate data to be marked on the workpiece, and/or to store data identifying the workpiece in relation to the marking. This system may operate automatically or semiautomatically. It is noted that, where gemstone classification automation is employed, a failsafe classification scheme will generally be employed which provides a manual classification or preclassification first. Thus, the risk of mismarking or misclassification will be reduced by the redundancy. The characteristics of the workpiece may be used to control parameters of the marking process.
Where a diamond having a polished girdle is to be marked, a single pass inscription is generally sufficient, and an automated optical feedback system may reliably control operation. However, the optical absorption of a smooth girdle on a diamond is low, so that a dye or ink coating is required to be placed on the surface, to ensure absorption of the laser energy. Where the girdle is rough, multiple passes of the inscription device may be necessary to generate a desired marking. The optical absorption of a rough girdle is generally high enough to dispense with the need for optically absorptive dyes or inks. While the execution of retries may be automated, user control may be desirable, and such control is possible through use of the video cameras which are directed at the workpiece, which display a real time image on a computer monitor.
An optically absorptive dye or ink may be manually applied to the workpiece, such as by a marking pen, or the application process may be automated by applying the dye to a workpiece surface to be marked, such as with a porous marking tip. Advantageously, these inks or optically absorptive dyes remain on the surface of the workpiece, and would not be expected to penetrate. In general, a dye is selected which may be easily removed after marking by use of a solvent, such as alcohol. The dye may be removed manually or through an automated process, such as wiping with a solvent saturated pad.
In another embodiment, relief inscriptions are possible by modulating the laser pulses or selectively multiply ablating or graphitizing the workpiece at desired positions. Such relief markings are generally not necessary for simple alphanumeric or digital code inscription, but may be useful for logos, pictorial works, antialiasing of raster images, binary of Fresnel-type optics, diffraction optic effects, anti-piracy or anti-copying provisions, or in other circumstances.
In systems provided with two video cameras, video profiling of the workpiece is possible, which may be used to determine an optimal position of the workpiece for marking without requiring focus checking at each location. The dual cameras also allow positioning and viewing on the same video screen, wherein the camera views are each provided as separate image windows. The cameras are useful for determining an appropriate marking location, ensuring laser beam focus, aligning the stone, and monitoring progress of the marking process.
The computerized control system allows versatility in the design, selection and implementation of graphic and font inscription. In a preferred embodiment, Borland fonts are employed. However, other fonts or combinations of fonts may also be employed, for example, Borland, postscript, TrueType, plotter, or other type fonts or typefaces may be employed. Further, the marking system may be set up to respond to Adobe Postscript, Microsoft Windows GDI, Macintosh QuickDraw, HP-GL, or other graphics standards.
A preferred laser system is a self-standing diode laser pumped Q-switched Nd:YLF laser with an internal frequency doubler. Such a system avoids the requirements of a relatively large YAG laser with large power supply and strict environmental control, an external frequency doubler, a water cooling system, large size and weight, inherent instability, and long optical path.
A green filter is provided on the output of the laser to selectively filter laser diode emissions, while allowing the green (530-540 nm) laser emissions to pass. The laser diode illumination is undesirable because it saturates the image on the vertical (Z-axis) camera screen in the laser spot area and prevents convenient viewing of the girdle and inscription.
The preferred translatable stage arrangement overcomes a typically limited range of optical movement of laser steering systems, requiring inscription operations in multiple segments, and provides good absolute positioning repeatability. However, according to some embodiments of the invention, other types of beam positioning apparatus may be employed, such as beam steering systems.
A marking may be provided on the stone for a number of reasons. First, it may be desirable to identify a stone if it is lost or mixed with other stones. The marking may also be used to identify source or origin. In this case, the marking may be taken at face value.
In some instances, however, a risk of forgery or simulation requires further security measures. Therefore, it may be desired to ensure that the stone was marked by an indicated entity, or that the stone corresponds to the marking applied thereto. This requires one of at least two possible schemes. First, that a characteristic of the stone be unique and very difficult to simulate. For example, certain dimensions or ratios of the gemstone are the subject of somewhat random variations, and thus have a somewhat uncontrolled range of values. Natural flaws and other characteristics are also generally random in nature, and thus also difficult to simulate. It is therefore unlikely that one stone will correspond to another stone, and it is unlikely that another stone can be made to identically correspond to the determined dimensions and ratios through manipulations.
According to one aspect of the invention, therefore, these difficult to reproduce characteristics are used as an integrity check for an encoded message. These characteristics may be measured or recorded, and stored. Advantageously, these measurements and characteristics may be derived from an image of the stone captured in conjunction with the marking process. In fact, by storing such images and providing a pointer to the image, e.g., a serial number, the measurements or characteristics to be compared need not be determined in advance. Therefore, according to such a scheme, the stone need only include a pointer to a record of a database containing the data relating to the stone to be authenticated. This allows information relating to characteristics of the stone, which may be difficult to repeatably determine or somewhat subjective, to be preserved in conjunction with the stone or an identification of the stone. As stated above, an image of the stone on a certificate of authenticity may be used to verify that the stone is authentic, while providing a tangible record of the identification of the stone.
Another scheme relies instead on the difficulty in identically copying an inscription, including subtle factors and interactions of the laser marking beam with the stone itself. Thus, the marking itself is self-authenticating. An attempt to copy the marking will likely fail because of the technological limitations on the laser marking techniques, and/or sufficient information to determine all of the encoding information.
Thus, to authenticate a stone, either the markings alone or the markings in conjunction with the characteristics or physical properties of the stone are analyzed. In one scheme, the markings inscribed on the stone include information which correlates with characteristics of the stone which are hard to duplicate, and which recur with rarity, allowing self-authentication. In other schemes, the marking inscribed on the stone identifies a database record stored in a repository, thus requiring communication with the repository to obtain the authentication information. The hand cutting process for gemstones makes it is difficult or impossible to identically duplicate all measurable aspects of a stone, especially in conjunction with other physical characteristics, such as natural flaws. Such physical properties may include, for example, the girdle width at predetermined locations. The location may be identified, e.g., by an inscribed marking or by an offset from a marking which is not apparent from an examination of the stone alone. For any given gemstone, one or more such locations may be stored, thus increasing the difficulty in simulating the measurement. Further, such measurements are generally easy to obtain or determine from the imaging system of the inscribing system.
Sophisticated techniques, such as Raman scattering analysis, are known which may provide unique information about a particular natural crystal structure. While the preferred system does not employ Raman scattering analysis, such analysis may be used in conjunction with embodiments of the invention.
According to a preferred embodiment, the authenticity of a stone is determined may be determined by use of a jeweler""s loupe to compare the actual stone to an image of the stone, such as may be provided on or in conjunction with a certificate of authenticity. Because each stone has varying characteristics, including the marking, details of the cut, and the relationship of the marking to the landmarks of the stone, the image serves as a fingerprint, making each stone essentially unique. The certificate, in addition to the image of the stone, may also include other information, such as an encrypted code, as discussed below. Thus, both the stone and the accompanying certificate may include identifying information.
Thus, the present invention also encompasses secure certificates, i.e., documents which are tamper and copy resistant, bearing an image of a marked stone, security features, and authentication features. Known secure documents and methods for making secure documents and/or markings are disclosed in U.S. Pat. Nos. 5,393,099; 5,380,047; 5,370,763; 5,367,319; 5,243,641; 5,193,853; 5,018,767; 4,514,085; 4,507,349; 4,247,318; 4,199,615; 4,059,471; 4,178,404; and 4,121,003, expressly incorporated herein by reference. U.S. Pat. No. 4,414,967, expressly incorporated herein by reference, discloses a latent image printing technique, which may be used to form an image of a workpiece. U.S. Pat. Nos. 5,464,690 and 4,913,858, expressly incorporated herein by reference, relate to certificate having holographic security devices.
In another scheme, a stone may be authenticated without the certificate of authenticity, e.g., by a typical jeweler employing simple tools, such as a jeweler""s loupe and telephone. Therefore, according to one embodiment of the invention, a jeweler uses a loupe to read an alphanumeric inscription, invisible to the naked eye, on a gemstone. The alphanumeric inscription, or a portion thereof, includes identifying information about the gemstone, e.g., a serial number, which is entered into an authentication system, e.g., by a telephone keypad. The characteristics of the stone, determined at or around the time of the marking process, are then retrieved from a database. In general, these stored characteristics may include grading, size, identification and possible location of flaws, and an image of the stone, including unique or quasi-unique features. Thus, for example, an image of the marking and stone or portions of the stone, e.g., surrounding landmarks of the stone may be stored. Some or all of these characteristics may then be provided to the jeweler, such as by voice synthesis, telefacsimile of the image, or otherwise. Where a certificate of authenticity is available, the certificate may be recreated and a facsimile transmitted to the jeweler, allowing verification of all information contained thereon. The jeweler then compares the retrieved metrics and indicia with those of the stone. If the stone corresponds to the stored information, the stone is likely genuine. If, on the other hand, the stone does not correspond to the stored information, it is possible that the stone is a forgery.
In another embodiment, the authentication system requests a series of measurements from the jeweler, which may be obtained by micrometer or reticle in a loupe, without providing the nominal values to the jeweler, so that no explanation is provided for a failure to authenticate, making forgery more difficult. Of course, the system may also employ more sophisticated equipment for measuring characteristics of the stone and for communications, including a fully automated analysis and communications system.
In another embodiment, the gemstone is self authenticating. Thus, instead of comparison with metric data stored in a database system, the marking inscribed on the stone itself includes an encrypted message containing data relating to characteristics of the stone. A number of different types of messages may be employed. For example, a so-called public key/private key encryption protocol, such as available from RSA, Redwood Calif., may be used to label the workpiece with a xe2x80x9cdigital signaturexe2x80x9d. See, xe2x80x9cA Method for Obtaining Digital Signatures and Public Key Cryptosystemsxe2x80x9d by R. L. Rivest, A. Shamir and L. Adelmann, Communications of ACM 21(2):120-126 (February 1978), expressly incorporated herein by reference. In this case, an encoding party codes the data using an appropriate algorithm, with a so-called private key. To decode the message, one must be in possession of a second code, called a public key because it may be distributed to the public and is associated with the encoding party. Upon use of this public key, the encrypted message is deciphered, and the identity of the encoding party verified. The data in the deciphered message includes a set of unique or quasi unique characteristics of the gemstone. Therefore, one need only compare the information from the decoded message with the stone to verify the origin of the gemstone and its authenticity. In this scheme, the encoding party need not be informed of the verification procedure. Known variations on this scheme allow private communications between parties or escrowed keys to ensure security of the data except under exceptional authentication procedures.
Typical encryption and document encoding schemes which may be incorporated, in whole or in part, in the system and method according to the invention, to produce secure certificates and/or markings, are disclosed in U.S. Pat. Nos. 5,426,700 (and Ser. No. 07/979,081); 5,422,954; 5,420,924; 5,388,158; 5,384,846; 5,375,170; 5,337,362; 5,263,085; 5,191,613; 5,166,978; 5,163,091; 5,142,577; 5,113,445; 5,073,935; 4,981,370; 4,853,961; 4,893,338; 4,995,081; 4,879,747; 4,868,877; 4,853,961; 4,816,655; 4,812,965; 4,637,051; 4,507,744; and 4,405,829, expressly incorporated herein by reference. See also, W. Diffie and M. E. Hellman, xe2x80x9cNew directions in cryptographyxe2x80x9d, IEEE Trans. Information Theory, Vol. IT-22, pp. 644-654, November 1976; R. C. Merkle and M. E. Hellman, xe2x80x9cHiding information and signatures in trapdoor knapsacksxe2x80x9d, IEEE Trans. Information Theory, Vol. IT-24, pp. 525-530, September 1978; Fiat and Shamir, xe2x80x9cHow to prove yourself: practical solutions to identification and signature problemsxe2x80x9d, Proc. Crypto 86, pp. 186-194 (August 1986); xe2x80x9cDSS: specifications of a digital signature algorithmxe2x80x9d, National Institute of Standards and Technology, Draft, August 1991; and H. Fell and W. Diffie, xe2x80x9cAnalysis of a public key approach based on polynomial substitutionxe2x80x9d, Proc. Crypto. (1985), pp. 340-349, expressly incorporated herein by reference.
Another encoding scheme uses a DES-type encryption system, which does not allow decoding of the message by the public, but only by authorized persons in possession of the codes. This therefore requires involvement of the encoding party, who decodes the message and assists in stone authentication.
In order to provide enduring authentication, it may be desired that multiple codes, containing different information in different schemes, be encoded on the gemstone, so that if the security of one code is breached or threatened to be breached, another generally more complex code, is available for use in authentication. For example, a primary code may be provided as an alphanumeric string of 14 digits. In addition, a linear bar code may be inscribed with 128-512 symbols. A further 2-D array of points may be inscribed, e.g., as a pattern superimposed on the alphanumeric string by slight modifications of the placement of ablation centers, double ablations, laser power modulation, and other subtle schemes which have potential to encode up to about 1 k-4 k symbols, or higher, using multivalued modulation. Each of these increasingly complex codes is, in turn, more difficult to read and decipher.
The ablation pattern of the marking is subject to random perturbations due to both system limitations and surface variations of the stone. Thus, even with a self-authenticating code, it is generally desired to store image information relating to the stone in a database after the marking process is completed. This database may then be used for further verification or authentication by image comparison or feature extraction.
Thus, a number of authentication schemes may be simultaneously available. Preferably, different information is encoded by each method, with the more rudimentary information encoded in the less complex encoding schemes. Complex information may include spectrophotometric data, image information, and geometric dimensional topology. Thus, based on the presumption that deciphering of more complex codes will generally be required at later time periods, equipment for verifying the information may be made available only as necessary.
Known techniques for using ID numbers and/or encryption techniques to preventing counterfeiting of secure certificates or markings are disclosed in U.S. Pat. Nos. 5,367,148; 5,283,422; 4,494,381; 4,814,589; 4,630,201 and 4,463,250, expressly incorporated herein by reference.
It is also noted that information may also be stored holographically in crystalline matter. Therefore, in accordance with the present invention, authentication holographic data may be stored within a crystal. The techniques for forming and reading such holographically encoded messages are known, and the use of such encoded messages to authenticate gemstones is a part of the present invention. Thus, the information may be stored as a hologram within the crystalline structure of the stone, or as a relief or phase hologram on a certificate. Therefore, a hologram may be formed directly from the gemstone, preferably optically enlarged. Since the laser markings comprise ablation spots, these will be apparent in the hologram. Further, since the marking process includes a laser, this same laser may be used to expose the hologram, using a modified optical system. For example, a pair of chromate holograms may be individually formed for each gemstone, one placed on the certificate and the other stored with the originator of the marking. The certificate may also include known security features.
Where an original hologram of the workpiece is available, authentication may be automated by optically correlating the hologram and the workpiece. This method will be very sensitive to subtle changes in the workpiece, and thus particularly tamper proof. Preferably, the optical correlation pattern of the hologram and the workpiece is stored after generation or developing the final hologram, in order to compensate for any changes during processing. This optical correlation pattern may be stored photographically or digitally.
Therefore, it is a characteristic of this aspect of the invention that, in order to identify a gemstone, the information stored thereon identifies a database record relating to the stone, and including information relating thereto, or the stored information itself relates to characteristics of the stone.
In one aspect of the invention, the imaging system is ordinarily disposed to view both a portion of the girdle of the stone and a profile thereof. Therefore, it is generally desirable to derive the required information relating to the stone from the imaging system while the gemstone is mounted in the apparatus. Where the inscription itself includes encoded characteristics, these may be applied by the apparatus by imaging the stone through the imaging system, and applying an inscription based on the imaging system output, i.e., by using feedback positioning. An image of the inscribed stone may also be obtained and stored. As stated above, the inscription may be explicitly encoded with readily apparent information, such as an inscribed alphanumeric code, or may include covert information, such as ablation spot placement with respect to stone landmarks, beam modulation, spacing between distant ablation spots, and pseudorandom ablation markings. The markings may also include indicia made at critical portions to allow repeatable measurements, such as edge margins of the girdle.
According to one method of the invention, a gemstone to be marked is imaged, with the image analyzed and extracted information compared to information in a database. Preferably, the database is a central database, remote from the marking apparatus, and the stored information is in digital form. The image is compared to data relating to at least a subset of images of comparable gemstones. An encoded marking is then proposed for a location on the girdle of the stone which, is either absolutely unique, or unique when taken with an easily defined characteristic of the stone. The database system is employed to prevent identical markings on comparable gemstones, and thus fails to approve a proposed marking if it is too similar to any other stone in the database. Thus, according to this aspect of the invention, each stone has a unique coding, and only rarely will a stone be found which is capable of receiving an identical marking to a previously inscribed stone while meeting the same coding criteria. In a simple embodiment, the database assigns a unique serial number to each stone and prevents use of duplicate serial numbers. On the other hand, in a more complex scheme, serial numbers need not be unique if other characteristics of the stone may be used to distinguish candidates.
According to another aspect of the invention, the inherent limitations on the accuracy and repeatability of the marking process are employed to provide a unique encoding of a gemstone. Thus, the surface imperfections of the girdle and the ablation process itself interact to prevent a theoretically ideal marking. Because these effects may be due to vibration, power line fluctuations, laser instability and the like, they will tend to be random over a number of marking operations. These effects will also result from characteristics of the stone. Thus, an attempt to recreate a marking to a high level of detail, even with advanced equipment, will invariably be met with difficulty. Thus, by storing high resolution images of the actual marking, possibly including off axis images or defocused images to gain ablation depth information, authentication of the markings is possible.
In like manner, intentional or xe2x80x9cpseudorandomxe2x80x9d irregularities (seemingly random, but carrying information in a data pattern) may be imposed on the marking, in order to encode additional information on top of an a marking pattern. Such irregularities in the marking process may include beam modulation, double ablations, fine changes in ablation position, varying degrees of overlap of ablation locations, varying laser focus during pulses. Without knowledge of the encoding pattern, the positional irregularities will appear as random jitter and the intensity irregularities will appear random. Because a pseudorandom pattern is superimposed on a random noise pattern, it may be desirable to differentially encode the pseudorandom noise with respect to an actual encoding position or intensity of previously formed markings, with forward and/or backward error correcting codes. Thus, by using feedback of the actual marking pattern rather than the theoretical pattern, the amplitude of the pseudorandom signal may be reduced closer to the actual noise amplitude while allowing reliable information retrieval. By reducing the pseudorandom signal levels and modulating the pseudorandom signal on the actual noise, it becomes more difficult to duplicate the markings, and more difficult to detect the code without a priori knowledge of the encoding scheme.
While alphanumeric codes and other readily visible codes may be read by common jewelers, subtle encoding methods may require specialized equipment for reading. Therefore, another aspect of the invention provides an automated system for reading codes inscribed on a gemstone. Such a system operates as a video microscope with image analysis capability. The image analysis capability will generally be tuned or adapted for the types of coding employed, reducing the analysis to relevant details. Therefore, where a pseudorandom code appears in the ablation pattern, the individual ablation locations and their interrelations are analyzed. Likewise, where ablation depth or amplitude is relevant, confocal microscopy may be employed.
In like manner, a certificate of authenticity may be provided with authentication and security coding, to prevent forgery or counterfeiting. In addition to the techniques discussed above, a number of other known techniques are available for the tamper and copy protection of documents. In this case, the certificate adds an additional level to the security of the marking process. Therefore, while the workpiece preferably includes a secure marking which does not require a certificate of authenticity for authentication, the addition of the certificate eases the authentication process while making forgery more difficult.
A typical electronic reading device for a gemstone inscription will include a CCD imaging device with a high magnification lens, e.g., about 200 times magnification, and an illumination device. Apparent resolution of the CCD may be increased by multiframe averaging with slight shifts of the gemstone with respect to the CCD optical system. A computer system with a frame grabber or a tele-video system (e.g., a videoconferencing system) may be used to obtain the data and analyze it. In general, known image processing schemes may be used to extract the encoded information.
In addition to being analyzed for information content, i.e., the markings, the workpiece image may also be compared with an image stored in a database. Therefore, based on a presumptive identification of a gemstone, an image record in a database is retrieved. The image of the presumptive gemstone is then compared with the stored image, and any differences then analyzed for significance. These differences may be analyzed manually or automatically. Where a serial number or other code appears, this is used to retrieve a database record corresponding to the stone which was properly inscribed with the serial number or code. Where the code corresponds to characteristics of the stone and markings, more than one record may be retrieved for possible matching with the unauthenticated stone. In this case, the information in the database records should unambiguously authenticate or fail to authenticate the stone.
According to another aspect of the invention, the laser energy microinscribing system includes a semiconductor excited Q-switched solid state laser energy source, a cut gemstone mounting system, having an aperture, an optical system for focusing laser energy from the laser energy source, through said aperture onto a cut gemstone, a displaceable stage for moving said gemstone mounting system with respect to said optical system so that said focused laser energy is presented to desired positions on said gemstone, having a control input, an imaging system for viewing the gemstone from a plurality of vantage points, and a rigid frame supporting said laser, said optical system and said stage in fixed relation, to resist differential movements of said laser, said optical system and said stage and increase immunity to vibrational misalignments. By employing a laser system with low cooling and power requirements, the device may be made self contained and compact. By minimizing the size of the apparatus, and enclosing the device in a rigid frame or chassis, vibration immunity is improved. Thus, as compared to systems employing flashlamp excited lasers, substantial vibration isolation apparatus is eliminated.
According to another aspect of the invention, prior to any marking operation, the proposed marking and/or the presumed resulting image are compared to database records to determine if the proposed marking and/or resulting marked gemstone are too close to any previously marked gemstone to be easily distinguished. If so, the marking or proposed marking may be altered. In addition, as an automatic feature of the machine, this comparison may prevent use of an authorized machine to counterfeit a previously marked gemstone, and will insure the integrity of the database.
According to another aspect of the invention, a pattern marking is inscribed on a portion of the gemstone, such as a girdle. Because it is difficult to recreate a particular girdle pattern exactly, the pattern will allow, for example with a loupe, quantification of girdle characteristics, including width, contour and size. Thus, the pattern assists in providing a metric for gemstone authentication.
The database may be stored locally to the marking apparatus, but preferably a central database is maintained, receiving identification and/or image information from many remote marking locations, and allowing central control and retrieval of records. This also facilitates a separation of function to maintain the integrity of the system and long term authentication procedures.
It is therefore an object of the invention to provide a laser energy microinscribing system, comprising a pulse laser energy source; an workpiece mounting system, having an optical aperture; an optical system for focusing laser energy from the laser energy source, through said optical aperture onto a workpiece; means for directing said focused laser energy onto a desired portion of the workpiece, having a control input; and imaging system for viewing the workpiece from a plurality of vantage points; and input for receiving marking instructions; a processor for controlling said directing means based on said marking instructions and information received from said imaging system, to generate a marking in accordance with said instructions; and a storage system for electronically storing information relating to images of markings on a plurality of workpieces.
it is also an object of the invention to provide a method of microinscribing a workpiece with laser energy from a pulse laser energy source, focused by an optical system on the workpiece, comprising the steps of mounting a workpiece in a mounting system; directing the focused laser energy onto a desired portion of the workpiece; electronically imaging the workpiece from a plurality of vantage points; receiving marking instructions from an input; controlling the directing of the focused laser energy based on the marking instructions and the electronic imaging, to generate a marking in accordance with said instructions; and storing electronic information relating to images of markings on a plurality of workpieces.
It is a still further object of the invention to provide a laser energy microinscribing system, comprising a semiconductor excited Q-switched sold state laser energy source; a cut gemstone mounting system, having an aperture; an optical system for focusing laser energy from the laser energy source, through said aperture onto a cut gemstone; a displaceable stage for moving said gemstone mounting system with respect to said optical system so that said focused laser energy is presented to desired positions on said gemstone, having a control input; an imaging system for viewing the gemstone from a plurality of vantage points; and a rigid frame supporting said laser, said optical system and said stage in fixed relation, to resist differential movements of said laser, said optical system and said stage and increase immunity to vibrational misalignments.
These and other objects will become apparent. For a fuller understanding of the present invention, reference should now be made to the following detailed description of the preferred embodiments of the invention as illustrated in the accompanying drawings.